1. Field of the Invention
The present invention relates to an absolute angle detecting apparatus, and more particularly, to an absolute angle detecting apparatus that calculates an arc tangent (tan−1θ), on the basis of a sine signal and a cosine signal that are output from a magnetic sensor provided in a rotating body, and calculates the rotation angle of the rotating body on the basis of the arc tangent.
2. Description of the Related Art
A rotation angle detecting apparatus including a plurality of magnetic detecting elements that output a sine signal and a cosine signal corresponding to the relative rotation angle θ of a rotating body and an arithmetic unit that calculates an arc tangent on the basis of the sine signal and the cosine signal output from the plurality of magnetic detecting elements and then calculates a rotation angle between the rotating body and the magnetic detecting elements on the basis of the arc tangent has been proposed. For example, Hall elements or magnetoresistive elements are used as the magnetic detecting elements (for example, see JP-A-2006-47228 (FIGS. 1 to 4)).
The rotation angle detecting apparatus does not directly calculate the rotation angle of the rotating body from the sine signal and the cosine signal that are output from the magnetic detecting elements, but calculates an arc tangent on the basis of the sine signal and the cosine signal and then calculates the rotation angle of the rotating body on the basis of the arc tangent.
However, the rotation angle detecting apparatus including the plurality of magnetic detecting elements has a problem in that it is difficult to accurately calculate the rotation angle of a rotating body in the vicinities of switching positions due to positional deviation between the original switching positions and the switching positions of an arc tangent signal. That is, the switching positions of the arc tangent signal from a portion in which the arc tangent signal rises linearly to a portion in which the art tangent signal falls rapidly (for example, positions corresponding to angles of 0°, 180°, and 360° in FIG. 6). This is caused by, for example, a variation in the characteristics of the plurality of magnetic detecting elements, a variation in voltage applied to or output from each of the magnetic detecting elements, a variation in the phase of an output signal (a sine wave or a cosine wave) due to the misalignment of the magnetoresistive elements, and backlash of a speed increasing mechanism, as shown in FIG. 6.